多孔BN/Si3N4陶瓷表面Si3N4/Si2N2O涂层的设计制备与热震、透波性能研究

Based on the urgent requirement of novel wave-transparent materials in the development of high-mach flight aircraft radome and antenna window cover, the preparation of a double-layered structural composite ceramics was proposed in this project. A vacuum impregnation method assisted by subsequent heat-treatment was adopted to prepare Si3N4/Si2N2O coating on the porous BN/Si3N4ceramics with dense and uniform combination to the matrix. The porous BN/Si3N4 composite ceramics with Si3N4/Si2N2O coating can incorporate many excellent properties together such as moisture proof, enhancement and improvement on the usage temperature range of the material while the coated Si3N4/Si2N2O has little effect on the dielectric properties of the porous BN/Si3N4ceramic at the same time. The main contents of the project are as following: (1) Microstructure evolution mechanism and the reaction kinetics of the interface area between porous BN/Si3N4ceramicmatrix and Si3N4/Si2N2O coating. (2) Structural design of the double-layer composite ceramics and the wave-transparent mechanism analysis. (3) Characterization and evaluation methods of the double-layer structure composite ceramics under the conditions of thermal, force, moisture and other effects. This is a multi-disciplinary project involves materials science, material joining, mechanics, solid state physics and other disciplines. The project has a clear application background and integrates material structural design and preparation process together. Therefore, the proposal of this project has theoretical and practical significances for the development of structural design and novel preparation method of double-layered wave-transparent ceramic materials.

以高马赫数飞行器天线罩、天线窗用透波材料为研究背景，本项目提出一种通过真空浸渍辅助后续高温处理的方法，在多孔BN/Si3N4陶瓷表面制备致密、均匀且与基体结合良好的Si3N4/Si2N2O陶瓷涂层，进而实现双层结构复合陶瓷透波材料的制备，使涂覆涂层后的Si3N4基复合陶瓷兼具防潮、增强、提升材料使用温度范围、透波性能优良等特点。重点研究：(1) 涂层与基体界面微观组织结构的形成、演化机理以及反应动力学；(2) 双层结构Si3N4基复合陶瓷透波材料的结构设计方法及透波机理分析；(3) 双层结构Si3N4基复合陶瓷透波材料在热、力、汽等作用下损伤/失效行为的评价与表征。本项目涉及材料学、材料连接、力学、固体物理学等多个学科的交叉，不仅具有明确的应用背景特色，更是将材料的结构设计与制备融为一体，对于开拓双层结构复合陶瓷的结构设计与新型制备方法具有非常重要的理论意义和现实意义。

本项目以高马赫数飞行器天线罩、天线窗用透波材料为研究背景，提出了通过真空浸渍辅助后续高温处理的方法，在多孔BN/Si3N4陶瓷表面制备致密、均匀且与基体结合良好的Si3N4/Si2N2O陶瓷涂层，研究了浸渍和高温处理工艺对涂层与基体界面微观组织结构的形成、演化的影响，重点研究了表面涂层对双层结构Si3N4基复合陶瓷透波材料的力、热、介电、防潮等性能的影响，及其损伤机理。得到如下研究结果：.1）高温处理温度对于涂层物相组成有很大影响。当高温处理温度为1550 ℃、1600 ℃时，涂层的主要物相为α-Si3N4和β-Si3N4。升高温度至1650 ℃时，涂层主要物相为板状的Si2N2O和棒状的β-Si3N4。进一步提高处理温度达1700 ℃时，板状Si2N2O分解，其主要物相变为β-Si3N4。随着SiO2颗粒尺寸的增加，涂层中Si2N2O相的相对含量逐渐减少。反应活性高，分散均匀性好的硅溶胶更加适合作为SiO2的引入方式。.2）浸渍液中Si3N4与SiO2的摩尔比对于涂层物相组成有很大影响，从而影响了双层结构Si3N4基复合陶瓷透波材料的性能。随着Si3N4与SiO2摩尔比的增加，涂层中Si2N2O相的相对含量逐渐减少，双层结构复合陶瓷的介电常数有上升趋势，同时其抗氧化性能有所下降。与基体相比，双层结构复合陶瓷的介电常数增加，吸潮增重量明显下降，抗热震性能也有所改善，抗氧化性能和耐烧蚀性能提升显著。以上均表明，多孔BN/Si3N4复合陶瓷表面制备涂层后，能明显提高材料的抗粒子侵蚀能力，同时改善多孔材料的防潮性能。.本项目研究结果实现了双层结构复合陶瓷透波材料的制备，同时也实现了对多孔陶瓷基体的防潮、增强、提升耐高温性能等目标，将材料的结构设计与制备融为一体，对于开拓双层结构复合陶瓷的结构设计与Si3N4基复合陶瓷透波材料的发展具有非常重要的理论意义和现实意义。